1. Field of the Invention
The present invention pertains to musical tone generating device, and more particularly, to musical tone generating devices applicable to simulation of the sound of plucked string-instruments and rubbed string-instruments.
2. Prior Art
Various conventional musical tone generating devices exist, wherein tone generation elements thereof utilize waveform data stored in waveform memory for the generation of musical tones. The waveform data stored in waveform memory most commonly consists of digital representations of a plurality of fundamental waveforms. The data corresponding to one or more fundamental waveforms can be modified, combined and otherwise manipulated so as to generate any of a great number of more complex waveforms, whereby generation of a great variety of musical tones and simulation of many types of conventional non-electronic instruments become possible. Although considerably versatile, this variety of conventional musical tone generating device has certain limitations when applied to simulation of the sound of plucked string-instruments such as the guitar, or rubbed string-instruments such as the violin or cello. In particular, techniques entailing the use of feedback, and certain techniques effecting alteration of the harmonic spectrum of sound produced by a stringed instrument are not readily simulated with this type of conventional tone generating device.
In the repertoire of violinists, guitarists, and musicians playing certain other stringed instruments, special techniques exist whereby performers playing these stringed instruments can produce particular tonal and pitch variations. An example of such a technique is the harmonics playing method, wherein by lightly touching one or more strings at a position which is located at a point along the respective string or strings separated from the upper or lower fixation point thereof by a distance which is an integral fraction of the total length of the respective string or strings, i.e. 1/2, 1/3, 1/4, . . . of the total length thereof, variations in the harmonic makeup of the produced tones can be achieved when the corresponding string or strings are plucked or played with a bow. That is to say, a node is produced in the vibration of each string played in this way, whereby the intensity of the fundamental pitch and the intensity of particular harmonics of the fundamental pitch of the string or strings being played in this way are augmented or diminished.
In the above discussion, the lower fixation point of a string generally refers to where the string meets the bridge, whereas the upper fixation point refers to where the string meets the nut at the upper end of the finger board in the case of an open string. With a closed string, that is, a string which is being fingered and therefore has a fundamental pitch higher than that when the same string is open, the upper fixation point refers to the lowest fret against which the string is held in the case of a guitar, and the point on the finger board against which the string is being held in the case of a fretless instrument such as a violin.
Returning to the discussion of the harmonic playing method from a mechanistic point of view, a portion of vibrational waves propagating along a given string from the direction of the bridge of the instrument are reflected when they reach the point where the performer's finger is lightly in contact with the string, after which the reflected vibrational waves travel back again toward the bridge. The portion of the vibrational waves which travel past where the performer's finger is lightly in contact with the string continue as far as the upper fixation point of the string where they are then reflected downward in the direction of the bridge. A portion of the vibrational waves reflected downward from the upper fixation point are again reflected upward when they meet the performer's lightly touching finger, whereas the remainder continue on to the bridge. In this way three pathways are effectively formed over which vibrational waves circulate back and forth mutually interacting and interfering with one another, namely, the pathway formed between the upper fixation point and the lower fixation point, the pathway formed between the upper fixation point and the performer's lightly touching finger, and the pathway formed between the performer's lightly touching finger and the lower fixation point.
It can be seen from the above discussion that by employing techniques such as the harmonic playing method, in each string of a stringed instrument being played according to the method, the performer in effect establishes multiple pathways over which vibrational waves propagate and hence circulate. In that each pathway thus established in a given string shares a portion of its course with a portion of at least one other pathway in that string, each pathway in the string is in effect coupled either directly or indirectly with all of the other pathways formed in that string. In this way, constructive and destructive interaction takes place between the waves circulating in any pathway and those circulating in all of the other pathways of a given string, thereby leading to a rich harmonic spectrum in the audible tones finally created.
In addition to the above described harmonic playing method for stringed instruments, various other techniques and situation exist whereby coupling or feedback pathways are established. One example of such is the electric guitar, wherein the vibrations of strings being played are picked up with one or more magnetic pickups and converted therein to an electrical signal. The electrical signal is subsequently amplified and then output from one or more speakers as audible sound which can interact with the strings of the same guitar if sufficiently loud at the position where the guitar is located. At lower volumes, various types of interaction occur between the output of the speakers and the vibrating strings as well as other strings not damped by the performers hand, whereby alterations in the harmonic spectrum of the sound produced are generated. At a sufficiently high amplitude and if the speakers are sufficiently close to the guitar, a feedback loop is established leading to the generation of an oscillating component at a characteristic frequency which is included in the output signal from the guitar and amplified, thereby producing howling in the output of the speakers.
Due to the complexity and great variety of the underlying mechanisms whereby the above described special effects are achieved, these effects cannot readily be simulated using conventional musical tone generating devices which utilize waveform data for the generation of musical tones. Moreover, as stated in the Nyquist theorem, sampling of waveform data must be carried out at a rate twice the frequency of the highest frequency of which production thereof is desired. Accordingly, faithful reproduction of the harmonic spectrum produced by techniques such as the harmonic method requires sampling of waveform data at a very high rate in order to reproduce the highest frequency components thereof. For this reason, such a device would be considerably expensive due to need for additional processing power, high speed D/A converters and the like.
Additionally, using waveform data to simulate, for example, the above described harmonic method requires several times more waveform data than that of the conventional playing method for the same instrument. For which reason, in addition to the matters described in the preceding paragraph, implementation of such a device becomes very expensive.